Slide 1

C h a p t e r

The Heart

PowerPoint® Lecture Slidesprepared by Jason LaPres

Lone Star College - North Harris

publishing as Pearson Benjamin Cummings

Introduction to Cardiovascular System

The Pulmonary Circuit

Carries blood to and from gas exchange surfaces oflungs

The Systemic Circuit

Carries blood to and from the body

Blood alternates between pulmonary circuit andsystemic circuit

The Conducting System

Heartbeat

A single contraction of the heart

The entire heart contracts in series

First the atria

Then the ventricles

The Conducting System

A system of specialized cardiac musclecells

Initiates and distributes electrical impulsesthat stimulate contraction

Automaticity

Cardiac muscle tissue contracts automatically

The Conducting System

Structures of the Conducting System

Sinoatrial (SA) node - wall of right atrium

Atrioventricular (AV) node - junction betweenatria and ventricles

Conducting cells - throughout myocardium

The Conducting System

Conducting Cells

Interconnect SA and AV nodes

Distribute stimulus through myocardium

In the atrium

Internodal pathways

In the ventricles

AV bundle and the bundle branches

The Conducting System

Heart Rate

SA node generates 80–100 action potentialsper minute

Parasympathetic stimulation slows heart rate

AV node generates 40–60 action potentialsper minute

The Conducting System

The Sinoatrial (SA) Node

In posterior wall of right atrium

Contains pacemaker cells

Connected to AV node by internodalpathways

Begins atrial activation (Step 1)

The Conducting System

Figure 20–13 Impulse Conduction through the Heart

The Conducting System

The Atrioventricular (AV) Node

In floor of right atrium

Receives impulse from SA node (Step 2)

Delays impulse (Step 3)

Atrial contraction begins

The Conducting System

Figure 20–13 Impulse Conduction through the Heart

The Conducting System

Figure 20–13 Impulse Conduction through the Heart

The Conducting System

The AV Bundle

In the septum

Carries impulse to left and right bundlebranches

Which conduct to Purkinje fibers (Step 4)

And to the moderator band

Which conducts to papillary muscles

The Conducting System

Figure 20–13 Impulse Conduction through the Heart

The Conducting System

Purkinje Fibers

Distribute impulse through ventricles (Step 5)

Atrial contraction is completed

Ventricular contraction begins

The Conducting System

Figure 20–13 Impulse Conduction through the Heart

The Conducting System

Abnormal Pacemaker Function

Bradycardia: abnormally slow heart rate

Tachycardia: abnormally fast heart rate

Ectopic pacemaker

Abnormal cells

Generate high rate of action potentials

Bypass conducting system

Disrupt ventricular contractions

The Conducting System

Electrocardiogram (ECG or EKG)

A recording of electrical events in the heart

Obtained by electrodes at specific bodylocations

Abnormal patterns diagnose damage

The Conducting System

Features of an ECG

P wave

Atria depolarize

QRS complex

Ventricles depolarize

T wave

Ventricles repolarize

The Conducting System

Time Intervals Between ECG Waves

P–R interval

From start of atrial depolarization

To start of QRS complex

Q–T interval

From ventricular depolarization

To ventricular repolarization

The Conducting System

Contractile Cells

Purkinje fibers distribute the stimulus to thecontractile cells, which make up most of themuscle cells in the heart

The Cardiac Cycle

Cardiac cycle = The period between thestart of one heartbeat and the beginning ofthe next

Includes both contraction and relaxation

The Conducting System

The Cardiac Cycle

Begins with action potential at SA node

Transmitted through conducting system

Produces action potentials in cardiac muscle cells (contractilecells)

The Cardiac Cycle

Phases of the Cardiac Cycle

Within any one chamber

Systole (contraction)

Diastole (relaxation)

The Cardiac Cycle

Cardiac Cycle and Heart Rate

At 75 beats per minute

Cardiac cycle lasts about 800 msecs

When heart rate increases

All phases of cardiac cycle shorten, particularlydiastole

The Cardiac Cycle

Eight Steps in the Cardiac Cycle

1.Atrial systole

Atrial contraction begins

Right and left AV valves are open

2.Atria eject blood into ventricles

Filling ventricles

3.Atrial systole ends

AV valves close

Ventricles contain maximum blood volume

Known as end-diastolic volume (EDV)

The Cardiac Cycle

Eight Steps in the Cardiac Cycle

4.Ventricular systole

Isovolumetric ventricular contraction

Pressure in ventricles rises

AV valves shut

5.Ventricular ejection

Semilunar valves open

Blood flows into pulmonary and aortic trunks

Stroke volume (SV) = 60% of end-diastolic volume

The Cardiac Cycle

Eight Steps in the Cardiac Cycle

6.Ventricular pressure falls

Semilunar valves close

Ventricles contain end-systolic volume (ESV), about 40%of end-diastolic volume

7.Ventricular diastole

Ventricular pressure is higher than atrial pressure

All heart valves are closed

Ventricles relax (isovolumetric relaxation)

The Cardiac Cycle

Eight Steps in the Cardiac Cycle

8.Atrial pressure is higher than ventricularpressure

AV valves open

Passive atrial filling

Passive ventricular filling

Cardiac cycle ends

The Heart: Cardiac Cycle

The Cardiac Cycle

Blood Pressure

In any chamber

Rises during systole

Falls during diastole

Blood flows from high to low pressure

Controlled by timing of contractions

Directed by one-way valves

The Cardiac Cycle

Heart Sounds

S1

Loud sounds

Produced by AV valves

S2

Loud sounds

Produced by semilunar valves

S3, S4

Soft sounds

Blood flow into ventricles and atrial contraction

The Cardiac Cycle

http://www.med.umich.edu/lrc/coursepages/m1/anatomy2010/html/surface/thorax/heart_label.jpeg

The Cardiac Cycle

http://www.modernmedicine.com/modernmedicine/data/articlestandard/rnweb/342004/114145/r8a024ac101.jpg

The Cardiac Cycle

Heart Murmur

Sounds produced by regurgitation throughvalves

Cardiodynamics

The movement and force generated by cardiaccontractions

End-diastolic volume (EDV)

End-systolic volume (ESV)

Stroke volume (SV)

SV = EDV – ESV

Cardiac output (CO)

The volume pumped by left ventricle in 1 minute

Cardiodynamics

Cardiac Output

CO = HR X SV

CO = cardiac output (mL/min)

HR = heart rate (beats/min)

SV = stroke volume (mL/beat)

Cardiodynamics

Factors Affecting Cardiac Output

Cardiac output

Adjusted by changes in heart rate or stroke volume

Heart rate

Adjusted by autonomic nervous system or hormones

Stroke volume

Adjusted by changing EDV or ESV

Cardiodynamics

Atrial Reflex

Also called Bainbridge reflex

Adjusts heart rate in response to venousreturn

Stretch receptors in right atrium

Trigger increase in heart rate

Through increased sympathetic activity

Cardiodynamics

Hormonal Effects on Heart Rate

Increase heart rate (by sympatheticstimulation of SA node)

Epinephrine (E)

Norepinephrine (NE)

Thyroid hormone

Cardiodynamics

Factors Affecting the Stroke Volume

The EDV: amount of blood a ventricle contains at theend of diastole

Filling time:

–duration of ventricular diastole

Venous return:

–rate of blood flow during ventricular diastole

Cardiodynamics

The EDV and Stroke Volume

At rest

EDV is low

Myocardium stretches less

Stroke volume is low

With exercise

EDV increases

Myocardium stretches more

Stroke volume increases

Cardiodynamics

The Frank–Starling Principle

As EDV increases, stroke volume increases

Physical Limits

Ventricular expansion is limited by

Myocardial connective tissue

The cardiac (fibrous) skeleton

The pericardial sac

Cardiodynamics

End-Systolic Volume (ESV)

The amount of blood that remains in theventricle at the end of ventricular systole isthe ESV

Cardiodynamics

Afterload

Is increased by any factor that restricts arterialblood flow

As afterload increases, stroke volumedecreases

Cardiodynamics

Heart Rate Control Factors

Autonomic nervous system

Sympathetic and parasympathetic

Circulating hormones

Venous return and stretch receptors

Cardiodynamics

Stroke Volume Control Factors

EDV

Filling time

Rate of venous return

ESV

Preload

Contractility

Afterload

Cardiodynamics

Cardiac Reserve

The difference between resting and maximalcardiac output

Cardiodynamics

The Heart and Cardiovascular System

Cardiovascular regulation

Ensures adequate circulation to body tissues

Cardiovascular centers

Control heart and peripheral blood vessels

Cardiovascular system responds to

Changing activity patterns

Circulatory emergencies